River Perkerra catchment with an area of 1207 km 2 is drained by River Perkerra, which is one of the rivers flowing into Lake Baringo whose drainage area is 6820 km 2 . The lake is in a semi-arid area of Kenya. Its depth has reduced from 8 m in 1972 to 2.5 m in 2003 due to siltation resulting from high erosion rates in the catchment. The entire catchment is characterised by very steep slopes on the hillsides and gentle slopes in the middle and lower reaches where the surface is bare with very little undergrowth. Interventions to control soil erosion in this fragile ecosystem have been limited partly because of lack of data on erosion and its spatial distribution. In the present study, Universal Soil Loss Equation (USLE) was used in conjunction with GIS Arc/Info and Integrated Land and Water Information Systems (ILWIS) to estimate potential soil loss from River Perkerra catchment. Various physical parameters of the equation were derived by analysing spatial data and processing Landsat TM satellite imagery of the catchment. The estimated potential soil erosion from the catchment was 1.73 million tonnes/year while the sediment yield at the catchment outlet was found to be 1.47 million tonnes/year. The sediment delivery ratio derived using an empirical equation was 0.83. This figure indicates that a higher proportion of sediments generated in the catchment is delivered at the outlet. The use of GIS enabled the results of erosion potential to be mapped back onto the catchment. This is useful in identifying priority areas that require urgent management interventions in controlling soil erosion.

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This paper reports some findings of chemical as well as biochemical studies of Maerua subcordata plant juice extract. The studies include: chemical composition of the juice such as mineral contents, protein and polysaccharide contents. These tests were carried out both in the juice extracts and in the "flocs". The latter samples were analyzed to establish whether the material that settled as a result of clarification had minerals, protein and/or polysaccharides. While there were no significant amounts of minerals found in the juice or in the flocs, there were significant amounts of polysaccharides in the juice as well as in the flocs. However it was found that there were insignificant amounts of proteins in the settled flocs. This was indication that polysaccharides in the juice were precipitated along with the sediments present in water. Further biochemical experiments on the identity of polysaccharides which apparently aided flocculation indicated that they were of branched type, amylopectin. The paper attempts to explain the mechanism of sediments settling as aided by the plant juice components.

Two rainfall-runoff models were calibrated and regionalized using data from upper Ewaso Ng'iro drainage basin in Kenya. The two models were Nash Cascade-Diskin Infiltration (NCDI) model and Nash Cascade-Green Ampt Infiltration (NCGAI) model. Both models have physical and conceptual parameters. The former were derived from catchment characteristics by overlaying land cover and soil types within the framework of GIS. The latter were optimized using Schuffled Complex Evolution (SCE-UA) optimization algorithm. The conceptual parameters so determined were correlated with catchment physical parameters in a regionalisation process. This involved, in the case of suction at the wetting front and hydraulic conductivity, deriving the parameter values from soil texture. The remaining conceptual parameters were regionalised through stepwise optimization and adjustment of boundary conditions. The parameters realised were correlated with catchment characteristics through regression analysis in which values of R2 ranging from 0.92 to 0.99 were obtained. The regionalised models were then used to simulate runoff from the five catchments upon which satisfactory results were realised.

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